The present invention relates generally to mixing and dispensing guns for use in the plastic foam industry, and more particularly, to a design of gun which is adapted for easy, low cost mass production manufacture and which is capable of performing the functions needed for precise mixing and dispensing of thermosetting chemical products resulting from the mixture of two reactive chemical components.
In recent years, there has been an ever increasing use of polyurethane and like plastic foams for a number of applications. Urethane and related products, including isocyanurates silicones phenolics and epoxies, are well known as having a number of desirable characteristics. These include the potential for excellent heat insulation, compatability with low cost blowing agents, reproducability of chemical characteristics and excellent chemical and physical properties in the finished product.
Many urethane foams are resistant to degradation by many common solvents, moisture and atmospheric oxidation. Urethanes provide the best combination of heat insulation and physical strength for a given cost. The foam is naturally an adhesive material and bonds well to any number of substates In this connection, it can add structural strength to many articles wherein such strength is an important element. Fire retardance may be achieved easily with available formulations.
Moreover, urethane foams, being the reaction product of two individual components, may be varied in chemical composition for a number of purposes. Thus, urethane foams may be formulated so as to provide a finished product which is quite rigid, which is semi-rigid, or which is somewhat flexible and/or elastomeric. Foams of the kind in question may be made with almost exclusively closed cells, or with a desired proportion of open cells.
The types of products with which the instant invention is concerned are primarily the closed cell foam types of product used for insulation purposes in building structures and open the celled product used for packaging applications. The components of the foam are passed at high pressures above 40-50 p.s.i. through a gun which serves to meter and mix the components thoroughly in a nozzle from which they are discharged. According to the invention, chemicals components are taken directly to a job site in pre-pressurized cylinders, or shipped in bulk tanks requiring external pumps or other sound of pressurization. Here, the amount of product required to be dispensed is not so large as to require permanent, expensive equipment, as would be used in a factory. However, the amount of product used is significantly larger than could be accommodated by using small, individual aerosol cans, for example. The individual containers of the components carry from several pounds up to perhaps 25 to 50 or even more pounds or more of each component. These tanks are sufficiently portable to be moved about on the job site by one worker, but yet are able to provide sufficient foam to provide several hundred or thousand board feet of coverage.
With the ability of the chemical supply tanks to be moved about, there has been a significant demand for a dispensing gun which would provide the advantages and characteristics of low cost, operating flexibility and reliability in use.
One of these required characteristics is that the product be able to be mixed in a nozzle which can be used and then disposed of after use, and replaced with another nozzle at low cost for a succeeding job or succeeding phase of the job then being undertaken.
Another desirable characteristic is that the chemical products or constituents be able to be metered accurately and proportioned both as between themselves, and as a whole considering the desired dispensing rate.
A still further requirement of a gun of the type in question is that the valving be constructed and arranged so as to permit a proper proportioning action to be maintained even when the trigger is held completely opened or is opened within an intermediate range of positions to vary the discharge rate as desired.
An ideal gun, consequently, would be one which is able to be reliably manufactured at low cost and which will prevent premixing of the components, keeping them isolated from each other until they are discharged into the mixing chamber of an associated nozzle.
Another characteristic of such a gun would be the presence of a valve and trigger assembly which would permit this control, as well as provision of means for controlling the flow of components to the valve passages contained in the gun.
Another desirable characteristic of such a gun would be the ability to position a discharge nozzle correctly by "feel" and make it possible for the operator to insure himself that the nozzle is fully seated in a locked position before the gun is likely to be used.
Yet another desirable characteristic would be that as the ability to rapidly eject a used nozzle so that a new nozzle could be used in place thereof.
Another desirable characteristic would be a gun having the porting designed so as not to have any dead space for the accumulation of the chemicals in the port where they may be exposed to the atmosphere. Specifically, where the isocyanate component of the polyurethane would be allowed to have contact with atmospheric moisture (humidity) and react and crystallize in the port, rendering the gun inoperable.
Accordingly, it is a primary object of the present invention to provide an improved combination mixing and discharging gun for reactive chemical components, including a gun itself, or such gun combination with a disposable nozzle serving to mix and discharge the components being fed to it under the control of an operator-manipulated trigger.
Another object of the invention is to provide a gun which includes components which are easy to manufacture at low cost, incorporating a minimum number of components designed for mass production with no subcomponent assembly or remanufacture.
A still further object of the invention is to provide a gun which includes a valve assembly adapted to insure that the components are not mixed with each other prior to their discharge into the mixing chamber of the associated nozzle.
A still further object of the invention is to provide a valve arrangement which is adapted to promote mixing of the desired proportions of components at a variety of trigger or discharge rate settings.
Yet another object of the invention is to provide a gun which includes a number of easy-to-replace components, and wherein the stoichiometry of the product mixing may be changed or adjusted if desired without great inconvenience or expense.
Another object of this invention is to provide a unique valve component seating arrangement allowing for complete seating under high pressure without leakage.
A still further object of the invention is to provide a gun which includes plural low-cost individually replaceable components.
Another object of the invention is to provide a gun which requires a minimum of complex moving parts, and which is adapted to provide relatively foolproof operation in use.
Still another object of the invention is to provide a gun which is compatible with existing mixing and dispensing nozzles which are associated with the gun in use.
A still further object is to provide a gun wherein the valve provides positive product flow shutoff, and wherein the outlet passage or passage downstream of the flow control valve is extremely short and has close contact with the nipple ports of an associated nozzle.
The present invention achieves the foregoing and other objects and advantages by providing a gun having a gun body which includes a housing for component inlet and outlet passages and for a product flow control valve, which further includes a handle, a nozzle receiver assembly, and a trigger for rotating a spool valve between open, closed, and intermediate positions, and wherein means are provided for controlling the proportion and flow rates of the components within the flowing passages, and to facilitate insertion, locking, and ejection of the nozzle within the gun body.
The exact manner in which the foregoing and other objects and advantages of the invention are achieved in practice will become more clearly apparent when reference is made t the following detailed description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings, wherein like reference numbers indicate corresponding parts throughout.